1. Field of the Invention
The present invention relates to a process for the preparation of carboxylic acids from unsaturated fatty acids and/or their derivatives.
More precisely, the invention relates to a process for the preparation of monofunctional and difunctional aliphatic carboxylic acids from unsaturated fatty acids in the form of acid or of ester and more particularly in the form of triglyceride.
2. Description of the Prior Art
Various processes have been proposed for carrying out the preparation of carboxylic acids from unsaturated fatty acids.
A relatively old process described in U.S. Pat. No. 2,773,095 consists in performing the oxidation of the latter compounds by subjecting them to an oxidation with the aid of dilute nitric acid under pressure. The oxidation of oleic acid results in pelargonic acid and azelaic acid being obtained. However, the selectivity of the reaction conducted according to U.S. Pat. No. 2,773,095 is poor because an overoxidation is observed, resulting in the formation of lower monoacids and diacids.
Furthermore, it is known according to U.S. Pat. No. 2,865,937 to prepare mono- and dicarboxylic acids from unsaturated fatty acids, especially oleic acid, by subjecting the starting substrate to a scission by ozonolysis, followed by an oxidizing decomposition. A major disadvantage of this type of process is its prohibitive cost resulting from the use of ozone.
Another, equally costly, process is described in FR-A 2 101 729. An example of preparation mentions the oxidation of oleic acid with hydrogen peroxide, followed by hydrolysis with sulphuric acid, separation using solvent and another oxidation stage performed using a percarboxylic acid in the presence of metal ions. Besides the number of stages described, the high cost of the reactants engaged has to be noted.
None of these processes are satisfactory because they are difficult to transpose to an industrial scale, either because of poor reaction yields or for economic reasons.
The objective of the present invention is to provide a process enabling the abovementioned disadvantages to be avoided.